Cathode Ray Tube (CRT) displays typically include a screen that is sealed to a glass tube. The glass tube tapers to a neck region in which an electron gun is disposed. The electron gun is sealed within the neck region of the glass tube such that pins extend from the rear glass surface of the neck region. In operation, electrical power and input is coupled to the electron gun through the pins. The electron gun generates three electron beams that are scanned across the screen such that the beams strike phosphors that coat the inside of the screen. These phosphors then emit red, green, and blue light so as to generate a viewable display.
In a typical prior art process for manufacturing a CRT, once the CRT is assembled, a glass straw that extends from the rear glass surface of the CRT is used to evacuate the CRT. The glass straw is then melted, forming a seal that maintains a vacuum within the CRT. A protective cap is then typically placed over the pins for protecting the pins during subsequent process steps and during shipping, handling, and assembly into a final product. This protective cap is commonly referred to as a "base cap."
In one prior art process, high voltage electrical current is applied to the pins of the CRT to clean the electron gun. More particularly, some of the pins are coupled to ground and some are coupled to a high voltage electrical current. The electrical current arcs from charged regions to regions that are grounded, striking and vaporizing contaminant particles.
Such prior art methods require the application of a high voltage electrical current in order to effectively clean the CRT's electron gun. However, when surrounded by air, electrical arcing will occur between pins of the CRT's electron gun before the electrical current reaches the "high level" required to effectively clean the electron gun. This premature arcing also frequently results in damage to the CRT. To prevent such premature arcing between the pins of the CRT, prior art processes typically lower the neck of the CRT into a dielectric-fluid. However, air is often trapped between the protective cap and the stem base surface of the CRT. The trapped air allows for the deleterious premature arcing to occur between the pins on the outside of the CRT. This arcing produces heat, which, combined with mechanical stress resulting from the electric field between high voltage and positive ground, mechanically stresses the fillet glass, cracking the glass. This results in a defective CRT that must be scrapped. The resulting defective CRT's reduce manufacturing yield and result in increased manufacturing costs.
What is needed is an apparatus and method for cleaning an electron gun of a CRT that will reduce or eliminate the number of CRT's damaged during the cleaning process. Also, a method and apparatus is needed that meets the above requirement and that will prevent arcing between pins outside of the CRT during the cleaning process. The present invention provides an elegant solution to the above needs.